Conventionally, studies have been made of surface plasmon oscillation and of the Faraday effect, and it has been discussed to use these for various magneto-optical devices.
First, a description is given of surface plasmon oscillation.
When metal crystals are reduced in size into ultra-fine particles, surface plasma oscillation, which is characteristic of ultra-fine particles, occurs.
Conduction electrons in metal form a kind of plasma state with ion shells (each of which is part of an atom except an outer electron), and oscillation due to the collective motion of these electrons is referred to as plasma oscillation. The quantum of this plasma oscillation (waves regarded as a quantum) is referred to as plasmon.
Surface plasmon refers to a plasma mode localized on a surface.
Here, fine particles are so sized as to cause surface plasmon oscillation, and are normally in the range of several nm to several tens of nm in size depending on the material.
Next, a description is given of the Faraday effect of a magnetic body (material) on a periodic structure.
The plane of polarization of light that passes through a transparent ferromagnetic body (material) rotates. This phenomenon is referred to as the Faraday effect. The Faraday rotation angle is maximized when the light travels in a direction parallel to a spin orientation in the magnetic material.
It has been confirmed that if a thin film of this magnetic material is not provided as a flat film but is provided on a periodically uneven structure, the Faraday rotation angle is substantially greater than in the case of a flat film. (See, for example, below-described Patent Documents 1 and 2.) It is presumed that this is because the refractive index differs between the S wave and P wave of the transmitted light because of the periodic structure so as to cause a great difference in the ratio of amplitude, thus increasing the Faraday rotation angle in combination with the Faraday effect, which causes the plane of polarization to rotate. (See, for example, below-described Non-Patent Document).
This method of providing a magnetic body (material) on a periodic structure has the following problems.
While various methods of reversing the magnetization of a magnetic body have been proposed, it is considered necessary as a specific method to provide a coil as immediately as possible below the film (in order to effectively apply a generated magnetic field to the magnetic body) and generate a magnetic field by causing current to flow through the coil.
In this case, a greater number of coil turns increases magnetic field strength, but increases the number of interconnection layers and manufacturing cost. Therefore, it is considered to increase current while reducing the number of coil turns. In this case, it is preferable to apply a transparent conductive film such as ITO as interconnection material in terms of high transmittance. Such a transparent conductive film, however, has a problem in that a large current cannot be caused to flow therein because of its resistance, which is approximately ten times that of a copper line. That is, practically, it is necessary to cause a current of several hundred mA to flow in order to obtain a magnetic field strength of 100 gausses in a pixel of 100 μm in diameter, for example. Therefore, it has been necessary to apply a low-resistance metal line (of copper, silver, gold, or the like) although it is an opaque material.
As the coil is reduced in diameter, the magnetic field strength at the coil center increases. However, it is not possible to have a high aperture ratio (that is, light transmittance) without reducing interconnection line width. For example, in the case of forming a circular coil of a period of 100 μm (with a 10 μm distance between coils), the aperture ratio is approximately 60% with a copper line width of 10 μm.
Accordingly, it has been considered an ideal and an object to be achieved to perform driving with a small current using a transparent conductive film of high transparency.
[Patent Document 1] Japanese Patent No. 3628859
[Patent Document 2] Japanese Patent No. 3654553
[Non-Patent Document] Katsuragawa, T; “Enhancement of the Faraday Rotation,” Jpn. J. Appl. Phys., 40, 6365-636(2001)